The present invention relates to diaphragm elements in an electrolytic filter press assembly comprising anode and cathode compartments separated by diaphragms. The diaphragm elements comprise a frame, openings for the flow of gas and liquids, respectively, a diaphragm secured to the frame, sealing means and insulating means.
The electrolytic filter press assembly is primarily used for the production of hydrogen and oxygen from brines, usually aqueous alkali hydroxide solutions. Similar cells are used for the production of chlorine from sodium chloride solutions. Such cells can comprise steel frames or frames made of plastic materials. One advantage of using steel frames is that they are rigid, and large filter press assemblies can then be made. However, steel frames necessitate insulation and sealing devices between the frames. Corrosion is also a problem to be dealt with. One way of dealing with the corrosion problem is the nickel plating of, for instance, the surfaces of the diaphragm elements that are exposed to the brine or lye to be electrolyzed. But nickel plating is expensive and should be kept to a minimum.
Electrolyzers of the above type have been known for a long time and are described in numerous patens. In Norwegian patent No. 157024 there is described an electrolyzer of the filter press type for production of hydrogen and oxygen. Each cell consists of bipolar electrodes separated from each other by a diaphragm element. The cells are kept together between two end plates in such a way that the electrolytic cells are kept under constant pressure by longitudinal bolts between the plates. In the electrolyzer's longitudinal direction, and at its upper part, respective channels for hydrogen and oxygen, are made in the cells. At the lower part of the cells are channels for circulating lye.
From EP 0212240 A1 there is known an apparatus for electrolysis of solutions comprising bipolar elements made up of a conductive plate peripherally surrounded by an insulating frame provided with feeding and discharging channels along peripheral zones of the frame itself. Separating elements can be inserted between the bipolar elements, consisting of a porous diaphragm and an insulating frame also carrying feeding and discharging channels.